1. Field of the Invention
This invention relates to a novel structure for positioning an orifice for discharging a cleaning fluid jet inside a structure having a plurality of interconnected passages close to deposits to be removed from difficult to access passages inside the structure. More particularly, it relates to such a structure for reaching into steam generator tube bundles and similar assemblies for sludge breakup and removal in an improved manner.
2. Description of the Prior Art
The accumulation of sludge on the secondary side of pressured water reactor (PWR) steam generators in the nuclear power industry is an acute problem which has historically resulted in costly equipment maintenance, replacement and plant down-time. The sludge is a buildup of magnetite and copper compounds which originate in copper alloy condenser tubing and carbon steel condensate and feedwater piping. Removal of sludge is often difficult due to poor access and physical characteristics of the sludge material.
All presently used sludge lancing equipment depends on precise aiming of high pressure water jets from convenient, accessible locations within the typical steam generator. Such areas include the central blowdown lane and/or the annular area between the outer edge of the tube bundles and the internal diameter of the steam generator vessel. However, bare, high pressure water jets, traveling across distances of up to four feet or more have little chance for being delivered effectively to the location of the sludge, due to jet divergence, attendant loss of centerline velocity and interference caused by impact on tubes before the target sludge is reached. Documented success in removal of sludge using these techniques has been less than satisfactory, due primarily to the fact that a high pressure water stream quickly loses its energy as it leaves its high pressure nozzle orifice. As the jet's pressure dissipates in free space, its coherence, or tight focus, also degrades, severely reducing its material-erosion capability. A need therefore exists for improvement of sludge lancing techniques in steam generator tube bundles and similar difficult to access structures.